Radiation curing of unsaturated air-inhibited resins

ABSTRACT

An improved process for curing an unsaturated air-inhibited thermosetting resin with a vinyl compound copolymerizable therewith suitably by means of radiation with a beam from electron emitting means wherein curling occurs by the addition of unsaturated molecules one to another is described. The improvement is for reducing inhibition of the resin to surface cure and comprises: substituting for at least a fraction of the unsaturated inhibited resin a copolymer comprising a linear saturated backbone having pendant therefrom through linkage selected from the group consisting of ester, ether, urethane, amine, and amide, a plurality of ethylenically unsaturated groups capable of the addition. The copolymer is characterized in having an average molecular weight of between about 5,000 and about 225,000.

United States Patent Holicky et al. [4 1 Apr. 25, 1972 [s41 RADIATIONCURING 0F 3,414,498 12/1968 Shinohara et al. ..2o4/1s9.2 UNSATURATEDAIRJNHIBITED 3,317,635 5/1967 Osmond ..260/836 RESINS inventors: DonaldF. l-lolicky, Parrna; Roger P. Hill,

Mayfield Heights, both of Ohio Assignee: SCM Corporation, Cleveland,Ohio Filed: Feb. 11, 1969 Appl. No.: 798,469

References Cited UNITED STATES PATENTS 2/1970 Harthe ..204/159.l410/1969 Brooueetai. ..204/l59.14

Primary Examiner-Murray Tillman Assistant Examiner-Richard B. TurerAttorney-Harold M. Baum, Howard G. Bruss and Merton H. Douthitt 4 [S 7]ABSTRACT An improved process for curing an unsaturated air-inhibitedthermosetting resin with a vinyl compound copolymerizabletherewithsuitabiy by means of radiation with a beam from electronemitting means wherein curling occurs by the addition of unsaturatedmolecules one to another is described. The improvement is for reducinginhibition of the resin to surface cure and comprises: substituting forat least a fraction of the unsaturated inhibited resin a copolymercomprising a linear saturated backbone having pendant therefrom throughlinkage selected from the group consisting of ester, ether, urethane,amine, and amide, a plurality of ethylenically unsaturated groupscapable of the addition. The copolymer is characterized in having anaverage molecular weight of between about 5,000 and about 225,000.

7 Claims, No Drawings RADIATION CURING OF UNSATURATED AIR- INHIBITEDRESINS BACKGROUND OF THE INVENTION Many unsaturated thermosetting resinsexhibit inhibited curing at their air-contact surfaces. Such surfacesare softer than the interiors of the body of the resin and are thereforemore easily scratched, marred, and attacked by chemicals such as organicsolvents, acids, and alkalies. These qualities are disadvantageousinsofar as the integrity of the surface of the thermoset resinousproduct is concerned and are particularly undesirable when the resin isapplied to other surfaces as a film or coating. Attempts to overcome oravoid such inhibition to surface cure have been made, and U.S. Pat. No.3,210,441 to Dowling et al discloses that the presence of esterifiedresidues of monohydroxy acetals in certain polyester resins producesresins that are free of surface inhibition.

Recently, the polymerization of resinous materials by radiation has beensuggested. However, the use of this technique has resulted in the samedifficulty with many thermosetting resins, namely, inhibition of cure ofthe resin surface. Attempts which have been made to overcome inhibitionof cure of the resin surfaces irradiated in air by irradiating theresinous material in an inert gaseous atmosphere such as, for example,nitrogen, argon, krypton, etc., or in a vacuum have not been entirelysatisfactory.

During penetration by high energy radiation, the resinous materialundergoes an ionization effect which induces chemical reactionsincluding polymerization, and U.S. Pat. No. 2,863,812 to Grahamdiscloses that such radiation has not been found to have any appreciableionization effect at the exposed surface of irradiated material. Grahamattempted to overcome this'difficulty by having electrons pass throughan electrically conductive shield before impinging electrons upon thematerial to be radiated. Such manipulation increases and complicates theapparatus and process used for radiation. In accordance with the processof the present invention, it has been found possible to reduce oreliminate the inhibition to curing on the surface od cured air-inhibitedresins by substituting for at least a portion of the inhibited resin ahereinafter defined copolymer prior to irradiation.

The term air inhibited resin is used herein in its art recognized sense,that is, it means or refers to resins which when cured exhibitinhibition to complete surface cure whether the curing takes place inair, in a vacuum, or in an inert gaseous atmosphere such as nitrogen.

SUMMARY OF INVENTION The present invention provides an improved processfor cross-linking or curing an unsaturated air-inhibited resin with avinyl compound copolymerizable therewith by means of radiation with abeam from electron emitting means wherein the curing occurs by theaddition of unsaturated molecules one to another. The improvement is forreducing air-inhibition of cure of the surfaces of air-inhibited resinsand comprises: substituting for at least a fraction of said unsaturatedair-inhibited resin, a copolymer comprising a linear saturated backbonehaving pendant therefrom through linkage selected from the groupconsisting of ester, ether, urethane, amine, and amide, a plurality ofethylenically unsaturated groups capable of said addition. The copolymeris characterized in having an average molecular weight of between about5,000 and about 225,000. By so proceeding, inhibition of cure of thesurface of air-inhibited resins is significantly reduced or completelyeliminated.

While the use of high energy radiation has been found effective incuring or polymerizing thermosetting resins, its use has not overcomethe inhibition of surface cure of a wide variety of resins, particularlythermosetting unsaturated polyester resins in the presence of oxygen, avacuum, and in a large number of instances, nitrogen as well. Theresinous materials of the processes of the present invention are thosewhich are convertible by high energy radiation to higher molecularweight compositions and which possess an inhibition to such conversionin the presence of gases such as nitrogen and/or oxygen.

A wide variety of unsaturated resins suffer to a greater or a lesserdegree from this shortcoming. For example, partially curedpolybutadiene, polyisocyanate resins, and resins formed from styrene,methacrylates, acrylates, maleates, fumarates, etc., often exhibitair-inhibition. One specific air-inhibited resin is the condensationproduct of 3 mols of hydroxypropyl methacrylate and l mol ofhexamethoxymethyl melamine. The resulting product can be employed in theprocess of the present invention either as the condensation product perse or as further reduced with a vinyl compound such as, for example, avinyl monomer. The vinyl compound may serve as a solvent for the resinor, if desired, a non-reactive volatile fugitive solvent may be used.However, the process of this invention has its primary application inreducing inhibition of cure of unsaturated polyester resins, especiallywhen these are dispersed in or blended with one or more unsaturatedcompounds such as vinyl monomers which serve as cross-linking materials.

Unsaturated polyesters are well-known in the art and may be derived froma reaction between alcohols including glycols such as ethylene,propylene, butylene, diethylene, dipropylene, trimethylene, andtriethylene glycols, as well as polyols such as glycerol and/orerithrytol and unsaturated polybasic acids including maleic, 'maleicanhydride, fumaric, chloro maleic, itaconic, citraconic, mesaconicacids, etc.

Typical ethylenically unsaturated monomers include styrene, vinyltoluene, methyl methacrylate, a-methyl styrene, divinyl benzene,dichloro styrene, lower alkyl maleates, lower dialkyl fumarates,ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethyleneglycol diacrylate, diethylene glycol dimethacrylate, triethylene glycoldiacrylate, triethylene glycol dimethacrylate, tetraethylene glycolacrylate, tetraethylene glycol diacrylate, tetraethylene glycoldimethacrylate, trimethylol propane triacrylate, trimethylol propanetrimethacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate,hydroxypropyl acrylate, hydroxypropyl methacrylate, etc.

A minor amount, that is, up to 40 mol percent of the unsaturated acidcan be replaced with saturated and/or aromatic polycarboxylic acids ortheir chlorinated counterparts. Typical acids used in this instanceinclude phthalic, isophthalic, adipic, pimelic, glutaric, succinic,sebacic, chlorinated phthalic, tetrahydrophthalic, etc. A particularadvantage of radiation curing is a low temperature cure since little orno catalyst is included in the resin mix.

The foregoing resinous materials generally have an average molecularweight of about 6,000 and surfaces thereof are inhibited when cured bymeans of radiation in a vacuum, air, or in nitrogen atmospheres.

The term radiation as used herein is intended to include exposure to abeam from electron emitting means. It is also meant to include particleemission or electromagnetic radiation selected from the class consistingof ionizing particles, photons and combinations thereof. The radiationincludes particle emission and/or electromagnetic radiation. Where thebeam is one comprising particle emission, the particles can beelectrons, photons, neutrons, a-particles, and the like. Where the beaminvolves electromagnetic radiation, such radiation can be radio waves,microwaves, infrared waves, ultra-violet waves, X-rays, gamma rays, andthe like.

The energy of the electrons of the beam of radiant energy is an averageenergy of at least KEV. As a general guide, only that amount of energyneed be applied, that, in a particular case, completely penetrates andcures the resin within a time period at least comparable to that for aconventional heat activated reaction for the same material. Excessenergy is wasteful and also often results in undesired heating of theresin and the attendant radiation apparatus means with possible charringand other decomposition.

The amount of energy required depends on several factors such as themass of the resin, extent of prior cross-linking, if any, the distancebetween the radiation means (e.g., the energy source of the beam and theresin) and the like. The requisite amount of energy may readily bedetermined by trial and error variation of the above factors.

Suitable means or sources of radiation include conventional radio-activeelements such as radium, cobalt 60, strontium 90, X-ray machines andelectron accelerators. The latter may be of the type supplying fromabout 100 to about 300 KEV (thousand electron volts) at a currentbetween about to about 1000 milliamperes. British Pat. No. 949,191discloses that in most conventional commercial applications, otherradiation techniques or electron beams having an energy of between 500and 4000 KEV have been found especially suitable. The electrons of suchbeams have a useful penetration of between about 0.1 to about 0.7 inchin organic substances having a specific gravity of around one.

US. Pat. No. 3,247,132 issued to Burlant reports that the potential ofan electronic beam for radiation purposes may be in the range of about150,000 to about 450,000 (150-450 KEV) volts.

The terms microwave and microwave energy as used herein is meant toinclude electromagnetic wave energy of about 10 to l0 cycles per second.Microwaves can be generated by radio frequency power tubes such as themagnetron, ampletron, and klystrom. Their frequencies range between 300and 300,000 megahertz (MHz). One megahertz is equal to 10 cycles persecond. A typical microwave generator which may be employed as means ofradiation is described in US. Pat. No. 3,216,849 issued to Jacobs.Usually a 10 to 50 second exposure to microwaves is sufficient forcuring a resinous material, the time being in proportion to theintensity of the microwaves.

The linear copolymer which is substituted for at least a fraction of theunsaturated air-inhibited resin comprises a linear saturated backbone,the product of addition polymerization. The backbone has pendanttherefrom through linkage selected from the group consisting of ester,ether, urethane, amine and amide, a plurality of ethylenicallyunsaturated groups which are capable of addition polymerization withthemselves or with a copolymerizable vinyl monomer. Substitution of atleast about 5 weight percent of the polymer will result in a productwhich will, when exposed to a beam of radiation, cure or cross-link toform a cured product in which the inhibition to surface cure has beensignificantly reduced and the surfaces are more resistant to chemicalattack by solvents, acids, and alkalies than are the surfaces of curedconventional air-inhibited resins.

The substituted polymer may be any of the class above described. Wherethe plurality of ethylenically unsaturated groups of the substitutedcopolymer are attached to the saturated backbone through ester linkage,the ethylenically unsaturated groups will be residues of anethylenically unsaturated acid anhydride, an ethylenically unsaturatedacyl halide, an ethylenically unsaturated oxirane, or an ethylenicallyunsaturated hydroxyl substituted compound, and the copolymer backboneprior to the pendancy of the plurality of ethylenically unsaturatedgroups will be formed to include a monomer having hydroxyl, carboxyl,oxirane, or halide substituents which will be reactive withethylenically unsaturated compounds to effect the pendancy of theplurality of ethylenically unsaturated groups to the polymer backbone.

Where the plurality of ethylenically unsaturated groups of thesubstituted copolymer are attached to the saturated backbone throughether linkage, the. unsaturated groups will be residues of anethylenically unsaturated ether, ethylenically unsaturated halide, orethylenically unsaturated oxirane compound, and thebackbone prior to thependancy of the ethylenically unsaturated groups will have a pluralityof ether, hydroxyl, oxirane, or halide substituents to make the backbonereactive with an ethylenically unsaturated compound.

Where the plurality of ethylenically unsaturated groups of thesubstituted copolymer are pendant from the saturated backbone throughurethane linkage, the plurality of ethylenically unsaturated groups willbe residues of an ethylenically unsaturated isocyanate or ethylenicallyunsaturated hydroxyl substituted compound, and the backbone prior to theattachment of the plurality of ethylenically unsaturated groups willcontain a plurality of hydroxyl or isocyanate substituents to make thebackbone reactive with an ethylenically unsaturated compound.

Where the substituted polymer contains a plurality of ethylenicallyunsaturated groups which are attached to the saturated backbone throughamine linkage, the ethylenically unsaturated groups will be residues ofamine or oxiranes, and the backbone prior to the pendancy of theplurality of ethylenically unsaturated groups will contain a pluralityof amine or oxirane substituents.

Where the substituted polymer comprises a saturated backbone havingpendant therefrom through amide linkage a plurality of ethylenicallyunsaturated groups, the ethylenically unsaturated groups will beresidues of ethylenically unsaturated amines, ethylenically unsaturatedamides, and ethyleni cally unsaturated aldehydes and the linear backboneprior to the attachment of the plurality of ethylenically unsaturatedgroups will contain a plurality of reactable substituents such asisocyanate, amide or aldehyde.

The saturated linear backbone of the substituted polymer is an additionpolymer and can be formed from a wide variety of ethylenicallyunsaturated monomers, provided that one of the monomers contains afunctional substituent that will react with a reactable ethylenicallyunsaturated monomer to form an ester, ether, urethane, or amide linkage.The backbone is thus the copolymer of at least one unsubstitutedethylenically unsaturated monomer and an ethylenically unsaturatedmonomer containing a hereinafter defined functional substituent.

Ethylenically unsaturated monomers other than those containingfunctional substituents which can form the linear saturated backbone aremonomers selected from the class consisting of ethylenically unsaturatedsubstituted and unsubstituted hydrocarbons, ethylenically unsaturatedesters of organic and inorganic acids, ethylenically unsaturated organichalides, and ethylenically unsaturated nitriles.

Ethylenically unsaturated hydrocarbons which can form a portion of thepolymer backbone include aliphatic hydrocarbons, for example, ethylene,propylene, butylene, amylene, hexalene, heptylene, octylene, and thelike. Also included among ethylenically unsaturated hydrocarbons arearomatic hydrocarbons, particularly vinyl and vinylidene hydrocarbonsincluding styrene, a-methyl styrene, vinyl toluene, etc., and theirhalo-substituted counterparts.

Ethylenically unsaturated esters of organic and inorganic acids whichcan form a part of the saturated polymer backbone include esters ofunsaturated carboxylic acids, for example, the alkyl acrylates, such asethyl acrylate, propyl acrylate, butyl acrylate, ethyl hexyl acrylate,the corresponding methacrylates, and crotonates, etc. Also included areesters of ethylenically unsaturated alcohols and organic and inorganicacids, for example, vinyl acetate, vinyl butyrate, etc. Ethylenicallyunsaturated organic halides which can form a portion of the polymerbackbone include the aforementioned vinyl halides such as vinyl andvinylidene chloride, vinyl bromide, etc., and halo-substituted aromatichydrocarbons such as, for example, chloro styrene, bromo styrene, chloromethyl styrene, chloro bromo styrene, and the like.

Examples of ethylenically unsaturated nitriles which can form a portionof the saturated backbone of the linear polymers include acrylonitrile,methacrylonitrile, crotonitrile, and the like.

The backbone can contain at least one and sometimes more of the monomersfalling within the above-mentioned classes. However, the backbonepolymers must also contain at least one substituted ethylenicallyunsaturated monomer having the functional substituents hereinbeforedefined.

The terms functional monomer and functional substituents as used hereinare intended to mean and to refer to monomeric compounds or polymerscontaining hydroxyl, oxirane, carboxyl, carboxylic acid anhydride,isocyanate, ether, amine, or amide substituents.

The term unsaturated functionality" as used herein is intended to meanand to refer to monomers having ethylenic unsaturation as well as theunsaturation monomer residues comprising the plurality of theunsaturated pendant groups attached to the linear saturated ester-freebackbone.

Monomers which can be employed to form a portion of linear polymerbackbones containing hydroxyl functionality prior to attachment of theplurality of ethylenically unsaturated groups include, for example,ethylenically unsaturated alcohols, such as allyl, crotyl, a-methylallyl, B-methyl crotyl allyl alcohols, and the like.

Monomers other than ethylenically unsaturated alcohols which can beemployed include hydroxy substituted lower alkyl esters of a,B-ethylenically unsaturated carboxylic acids. Advantageously, hydroxylower alkyl esters containing from about two to about five carbon atomsin the alkyl group can be employed. Although hydroxyalkyl esters ofethylenically unsaturated carboxylic acids can contain more than aboutfive carbon atoms in the alkyl group, employment of such esters is notusually advantageous and their use can sometimes be economicallyunfeasible.

Both hydroxyalkyl esters of ethylenically unsaturated monoanddicarboxylic acids can be suitably employed. Examples of esters ofmonocarboxylic acids include hydroxyalkyl esters of acrylic, crotonic,isocrotonic, vinyl acetic, methacrylic, tiglic, angelic, senecioic,teracrylic, hypogeic, oleic, elaidic, erucic, brassidic, and behenicacids. Of these, hydroxyethyl, hydroxypropyl, and hydroxybutyl esters ofacrylic, vinyl acetic, and methacrylic acids are preferred for economicreasons. Examples of hydroxyalkyl esters of unsaturated dicarboxylicacids include esters of fumaric, maleic, glutaconic, citraconic,itaconic, ethidene malonic, mesaconic, allyl malonic, propylidenemalonic, hydromuconic, pyrocinconic, allyl succinic, carbocaprolactonic,and teraconic acids. Of these, hydroxyethyl, hydroxypropyl, andhydroxybutyl diesters of maleic and itaconic acids are preferred becauseof the low cost and availability of these esters.

Hydroxy lower alkyl esters which have been found to provide particularlyadvantageous linear polymers are hydroxyethyl acrylate, hydroxypropylacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate,dihydroxyethyl fumarate, dihydroxypropyl fumarate, dihydroxyethylmaleate, and dihydroxypropyl maleate.

When such esters are copolymerized with vinyl monomers such as styrene,ethyl acrylate, methyl methacrylate, acrylonitrile, methacrylonitrile,or crotonitrile, a saturated linear ester-free addition polymer isformed consisting of a backbone containing a plurality of hydroxylgroups.

As will be evident to those skilled in the art, a wide variety ofethylenically unsaturated monomers capable of forming ester groups withthe pendant hydroxyl groups of the abovedescribed copolymer backbone canbe employed. Such ethylenically unsaturated compounds includeethylenically unsaturated carboxylic acids, ethylenically unsaturateddicarboxylic acid anhydrides, ethylenically unsaturated acyl halides,and the like.

Examples of ethylenically unsaturated carboxylic acids include those ofthe acrylic series hereinbefore described.

Examples of ethylenically unsaturated dicarboxylic acid anhydridesinclude maleic and itaconic anhydrides.

Examples of unsaturated acyl halides include acrylyl chloride or bromideand methacrylyl chloride or bromide.

The substituted polymers of this invention are usually dispersed in avinyl monomer and are conventionally stabilized through the addition ofknown inhibitors, for example, hydroquinone, to prevent them fromcross-linking during storage.

Substituted copolymers wherein the saturated linear backbone, prior tothe addition of the plurality of ethylenically unsaturated groupsthereto, contains a plurality of pendant oxirane groups are additionpolymers of any of the unsubstituted unsaturated monomers plus anethylenically unsaturated glycidyl compound, for example, glycidylacrylate, glycidyl methacrylate, allyl glycidyl ether, and monoglycidylmaleate. In such polymer, the plurality of ethylenically unsaturatedgroups are residues of a, B-ethylenically unsaturated substituted andunsubstituted carboxylic acids.

Substituted resins wherein the linear backbone prior to the addition ofethylenically unsaturated groups thereto contains a plurality of pendantdicarboxylic acid groups are the addition polymers of any of theaforementioned unsubstituted ethylenically unsaturated monomers plus anethylenically unsaturated dicarboxylic acid anhydride, for example,maleic, or itaconic anhydride, and the plurality of ethylenicallyunsaturated groups are residues of hydroxyl substituted ethylenicallyunsaturated compounds, for example, any of the ethylenically unsaturatedalcohols hereinbefore described or residues of hydroxyl substitutedlower alkyl esters of a, B-ethylenically unsaturated carboxylic acids.The plurality of ethylenically unsaturated groups are pendant from thebackbone through ester linkage. 1

Where the substituted copolymers are composed of a saturated linearester-free backbone having a plurality of ethylenically unsaturatedgroups pendant therefrom through urethane linkage, the backbone prior tothe pendancy of the ethylenically unsaturated groups thereto willcomprise the linear addition polymer of one or more of theaforementioned unsubstituted monomers in addition to an ethylenicallyunsaturated isocyanate.

Examples of ethylenically unsaturated isocyanates which can be employedto form a portion of the polymer backbone include, for example, allylisocyanate, isopropenyl isocyanate, 4-isocyanato styrene, vinylnapthalene isocyanate, S-isocyanato pentene-l, and the like. Otherunsaturated isocyantes are isocyanate esters of a, B-ethylenicallyunsaturated carboxylic acids, and include bis-(2-isocyanato-ethyl)fumarate, bis- (2-isocyanato-ethyl) maleate, isocyanato ethyl acrylate,isocyanato propyl methacrylate, l-methyl benzene-2-isocyanato-4-carbamic ester propyl methacrylate, bis-( 2-isocyanato-lmethylbenzene-4-carbamic ester propyl) maleate, and the corresponding fumarateesters, etc.

The three last-mentioned esters are unsaturated urethane esters having aterminal isocyanate group. The plurality of ethylenically unsaturatedgroups are appended to the backbone by reacting an unsaturated hydroxysubstituted compound, for example, any of the hydroxy substitutedethylenically unsaturated compounds hereinbefore described. There isthus formed a copolymer comprising a linear saturated backbone havingpendant therefrom through urethane linkage a plurality of ethylenicallyunsaturated groups Substituted polymers similar to those described abovein that they have a plurality of ethylenically unsaturated groups whichare pendant from the backbone through urethane linkage can also beprepared from linear polymer backbones which have prior to the pendancyof the unsaturated groups a plurality of hydroxyl groups. In thisinstance, the pendant groups will be residues of ethylenicallyunsaturated isocyanates.

Substituted copolymers containing a saturated linear backbone havingpendant therefrom an ethylenically unsaturated ether are prepared byforming a backbone having the plurality of ether, hydroxyl or oxiranegroups. Where the backbone prior to the attachment of the plurality ofethylenically unsaturated groups contains a plurality of pendant ethersubstituents, the plurality of ethylenically unsaturated groups areresidues of ethylenically unsaturated ethers which are attached to thebackbone through transetherification reaction.

Typical unsaturated ethers are methyl vinyl ether, ethyl vinyl ether,propyl vinyl ether, butyl vinyl ether, allyl vinyl ether, phenyl vinylether, etc. Transetherification can be readily accomplished by heating astoichiometric quantity of a hydroxy substituted ethylenicallyunsaturated compound such as those hereinbefore described in thepresence of an acidic catalyst, for example, a Lewis acid catalyst.

Substituted copolymers containing a plurality of ethylenicallyunsaturated groups pendant through ether linkage can also be preparedfrom saturated linear polymer backbones containing prior to theattachment of the ethylenically unsaturated groups a plurality ofpendant oxirane substituents. In this instance, the plurality ofethylenically unsaturated groups will be residues of ethylenicallyunsaturated hydroxyl substituted compounds hereinbefore described.

Conversely, the substituted polymers in which the plurality ofethylenically unsaturated groups are residues of ethylenicallyunsaturated oxiranes can also be prepared from saturated polymerbackbones containing prior to the attachment of the groups a pluralityof pendant hydroxyl substituents.

Substituted polymers containing a plurality of ethylenically unsaturatedgroups pendant through amine linkage are prepared by forming a backbonefrom unsubstituted monomers and an ethylenically unsaturated aminecontaining at least one hydrogen atom such as, for example, n-methylamino methacrylate, n-methyl allyl amine, n-ethyl amino acrylate,n-propyl amino ethyl hexyl acrylate, etc. The resultant linear polymeris comprised of a saturated ester-free backbone and contains a pluralityof amine groups attached and external to the backbone. The plurality ofethylenically unsaturated groups which can be appended to the backboneinclude residues of ethylenically unsaturated isocyanates, esters ofisocyanates, ethylenically unsaturated halides, and ethylenicallyunsaturated glycidyl compounds similar to those hereinbefore described.

Substituted copolymers containing a plurality of ethylenicallyunsaturated groups external to and pendant from the backbone throughamide linkage are prepared by including in the saturated linear polymerbackbone an ethylenically unsaturated amide, for example, acrylamide,methacrylamide, crotoamide, orthovinyl benzamide, meta-vinyl benzamide,etc., and the plurality of ethylenically unsaturated groups are residuesof ethylenically unsaturated aldehyde compounds. Such polymers can alsobe prepared by forming a backbone containing pendant amine or isocyanategroups and reacting the amine groups with ethylenically unsaturatedisocyanates or reacting the pending isocyanate substituents withethylenically unsaturated amines.

Generally the polymers which may be substituted or partially substitutedfor the air-inhibited resins which are subsequently cured by radiationas herein described comprise a class of linear copolymers consistingessentially of a linear saturated ester-free backbone having pendanttherefrom through a linkage selected from the group consisting of ester,urethane, ether, amine, or amide a plurality of ethylenicallyunsaturated groups, said copolymer being polymerizable with vinylmonomer for thermosetting purposes wherein the backbone is the additionpolymer of:

A. from about 40 to about 90 weight percent of at least one monomerselected from the group consisting of l. mono ethylenically unsaturatedsubstituted and unsubstituted hydrocarbon 2. mono ethylenicallyunsaturated esters of organic and inorganic acids 3. halides of monoethylenically unsaturated alcohols 4'. mono ethylenically unsaturatednitriles and g B. from about l to about 20 weight percent of an a, B-mono ethylenically unsaturated mono functional monomer selected from theclass consisting of hydroxyl substituted compounds, oxiranes,isocyanates, ethers, amides, and primary and secondary amines; and wheresaid ethylenically unsaturated groups are pendant from said backbone byvirtue of the reaction of a substantially stoichiometric amount of a,B-mono ethylenically unsaturated mono functional monomer reactible withthe functional groups pendant from the backbone.

The above-described polymers can be prepared by a process whichcomprises the steps of:

A. forming a reaction mixture consisting essentially of a liquid organicdiluent B. from about 40 to about weight percent, basis the weight ofthe polymer backbone, of at least one monomer selected from the groupconsisting of l. a, B-ethylenically unsaturated substituted andunsubstituted hydrocarbons 2. an a, ,B-ethylenically mono unsaturatedoxirane,

3. an a, B-ethylenically mono unsaturated hydroxyl substituted compound4. an a, fl-ethylenically mono unsaturated monoisocyanate 5. an a,B-ethylenically mono unsaturated primary or secondary amine 6. an a,B-ethylenically mono unsaturated amide;

C. a free-radical catalyst; heating said mixture with agitation in aninert atmosphere and for a time sufiicient to form a linear saturatedester-free addition polymer containing polar functionality and selectedfrom the class consisting of ether, oxirane, hydroxyl, isocyanate,amine, and amide groups, said polar functionality being external to saidbackbone, said polymer being dispersed in said diluent,

D. adding to thedispersion so formed 1. when said backbone containsetheral functionality, a substantially stoichiometric amount of a monohydroxy-substituted a, B-ethylenically mono unsaturated compound and anacidic catalyst, thereby'forming said copolymer having a plurality ofpendant ethylenically mono unsaturated groups external to the backboneand pendant therefrom through ether linkage;

2. when said'backbone contains an ethylenically unsaturated oxirane, asubstantially stoichiometric amount of an a, B-ethylenically monounsaturated monofunctional monomer selected from the group consisting ofan ethylenically unsaturated hydroxy compound, ethylenically unsaturatedprimary or secondary amine, and an ethylenically unsaturated amide,thereby forming said copolymer wherein the plurality of ethylenicallyunsaturated groups are pendant from the polymer backbone through etherlinkage when the unsaturated monomer is an ethylenicallyunsaturatedhydroxy compound, through amine linkage when theethylenically unsaturated monomer is an ethylenically unsaturated amine,and through amide linkage when the ethylenically unsaturated monomer isan amide;

3. when said backbone contains hydroxyl functionality, a substantiallystoichiometric amount of an a, B-ethylenically mono unsaturated monofunctional glycidyl compound thereby forming a backbone containing aplurality of ethylenically unsaturated groups pendant from said backbonethrough ether linkage external to said compound;

4. when said backbone contains amine functionality, a substantiallystoichiometric amount of an a, B-ethylenically mono unsaturated monofunctional monomer selected from the group of mono unsaturated monoisocyanates and ethylenically unsaturated oxiranes whereby the pluralityof said unsaturated groups are pendant from the backbone through aminelinkage;

5. when said backbone contains amide functionality, a substantiallystoichiometric amount of an a, B-mono ethylenically unsaturated monofunctional compound selected from the group consisting of ethylenicallyunsaturated aldehydes and ethylenically unsaturated oxiranes whereby theplurality of ethylenically unsaturated groups are pendant from thepolymer backbone through amide linkage;

6. when said backbone contains carboxyl or carboxyl anhydridefunctionality, a substantially stoichiometric amount of an a, B-monoethylenically unsaturated mono functional compound selected from thegroups consisting of hydroxyl substituted and oxirane compounds wherebythe plurality of ethylenically unsaturated groups are pendant from thepolymer backbone through ester linkage;

7. when said backbone contains isocyanate functionality, a substantiallystoichiometric amount of an a, B-mono ethylenically unsaturated monofunctional hydroxyl compound whereby the ethylenically unsaturatedgroups are pendant from the polymer backbone through urethane linkage.

E. heating the resultant mixture at a temperature and for a timesufficient to form a linear copolymer having a substantially inertbackbone ad containing pendant therefrom and external thereto aplurality of ethylenically mono unsaturated groups.

The polymers so obtained can be suitably used to provide a processimprovement in conventional processes for crosslinking unsaturatedair-inhibited resins with vinyl compounds copolymerizable therewith bymeans of radiation with a beam from electron-emitting means whereincuring occurs by the addition of unsaturated molecules one to another.The improvement of such air-inhibited resins and comprises substitutingfor at least a fraction of said unsaturated air-inhibited resin a linearcopolymer wherein the backbone is the addition polymer of:

A. from about 40 to about 90 weight percent of at least one monomerselected from the group consisting of 1. mono ethylenically unsaturatedsubstituted and unsubstituted hydrocarbons,

2. mono ethylenically unsaturated esters of organic and inorganic acids,3. 3. halides of mono ethylenically unsaturated organic alcohols, and

4. mono ethylenically unsaturated nitriles and B. from about 10 to about20 weight percent of an a, ,8- mono ethylenically unsaturated monofunctional monomer selected from the class consisting of oxiranes,ethers, hydroxyl compounds, isocyanates, amides, and primary andsecondary amines and where said ethylenically unsaturated groups arependant from said backbone by virtue of the reaction of a substantiallystoichiometric amount of an a, fl-mono ethylenically unsaturated monofunctional monomer reactible with functional groups pendant from thebackbone; said copolymer having an average molecular weight of fromabout 5,000 to about 225,000.

As noted hereinbefore, the molecular weight of the substitutedcopolymers is in the range of between about 5,000 and about 225,000 andthe substitution of the copolymers for the resin with the process ofthis invention, preferably is accomplished by employing copolymershaving an average molecular weight above the average molecular weight ofthe air-inhibited resin to insure significant reduction of inhibition ofsurface cure. Where the resin is an air-inhibited polyester, substitutedlinear copolymers having a molecular weight between 20,000 and 50,000have been found to be especially advantageous in reducing and/oreliminating air inhibition of the cured surface of thermoset products.

The amount of the air-inhibited resin fraction for which the copolymersare substituted can be at least about 5 weight percent of theunsaturated resin and will depend to a large extent on the tendency ofthe resin to exhibit air inhibition during or after cure.

Where the resin is one which, when cured, exhibits extreme lack of cureat its surface, the fraction substituted will be greater than in theinstance where the surface cure of the resin is partially inhibited.Advantageously, the linear copolymers can be substituted for frombetween about 20 to about 90 percent of the resin to provideair-uninhibited liquid thermosettable polymeric products.

Although the processes of this invention contemplate curing processesinvolving high energy radiation, the substituted compositions can alsobe cured by free radical catalysis and air inhibition is also reduced.However, the employment of high energy radiation has been found to beparticularly advantageous because it results in a low temperature curewherein polymerization reaction exotherms can be controlled and it hasbeen observed that high temperature cures sometimes tend to aggravate ormake more severe the air-inhibition of surface cure of air-inhibitedresins.

The invention thus provides an improved process for crosslinking anunsaturated air-inhibited resin with a vinyl compound copolymerizabletherewith wherein curing occurs by the addition of unsaturated moleculesone to another. The improvement is for reducing air-inhibition of theresulting cured surface when the process is conducted under normalair-inhibiting conditions and comprises substituting for at least afraction of the unsaturated air-inhibited resin or at least the surfaceportion thereof a copolymer such as those hereinbefore described andsubmitting the resultant mass to curing under air-inhibitedconditionsIThe curing process can thus be effected by using a freeradical catalyst, high energy radiation or high energy radiationfollowed by heat or microwave energy, or a combination of these curingmeans.

The following specific examples are intended to illustrate the inventionbut not to limit the scope thereof, parts and percentages being byweight unless otherwise specified.

EXAMPLE I To a 5 liter reaction vessel equipped with a thermometer, agas inlet valve, electrical heating coils, mechanical agitator, refluxcondenser, and inlet funnels for introducing inert gas and reactants,there was introduced 400 grams of xylene. Into a separate container,there was mixed under a blanket of nitrogen, 35 grams of styrene, 35grams methyl methacrylate, and 30 grams di(hydroxypropyl) maleate alongwith 4 grams of benzoyl peroxide. This mixture was charged into thereactor with continuous agitation over a period of 2 hours while thetemperature of the reactor contents was maintained at 285F. Prior to andduring the addition of the mixture to the reactor, gaseous nitrogen wascontinuously sparged through the reactor and the monomer mix. Thecontents of the reaction vessel were maintained under continuousagitation and at 285F. for 10 hours at which time substantially all ofthe styrene, methyl methacrylate, and dihydroxypropyl maleate mixturehad polymerized. The contents of the reaction vessel then consisted of adispersion of approximately grams of a linear polymer having a saturatedester-free backbone which contained hydroxyl groups pendant from andexternal to the backbone. A portion of the sample was withdrawn and theaverage molecular weight as determined by gel phase chromatography wasfound to be 75,000. The polymer had a hydroxyl number of 1 19.

The temperature of the contents of the reaction vessel was decreased to225F. and thereafter, 21 grams of maleic anhydride and a small amount oflithium carbonate were added over a period of about 60 seconds whileagitation was continued. Heating and agitation continued for 40 minutesuntil the maleic anhydride had reacted with the hydroxyl groups of thepolymer in the dispersion to form a polymer having pendant mono-maleategroups which contained terminal carboxyl functionality and ethylenicunsaturation which was converted to the hydroxypropyl half ester bypropylene oxide addition. Two hundred grams of the xylene were strippedfrom the polymer dispersion. One hundred grams of styrene whichcontained 0.030 weight percent of hydroquinone were added to the polymerdispersion. The remainder of the xylene was stripped providing a liquidpolymer composition containing 50 percent solids in which the solidsconsisted essentially of the saturated linear polymer backbone having aplurality of ethylenically unsaturated groups which were residues of thehalf ester ofhydroxy propyl maleate and were pendant through esterlinkage from the backbone. The linear polymer was dispersed in styrene.

The foregoing polymer was blended with a thermosetting polyester resinprepared by reacting equi-molar proportions of 1,3-propylene glycol andmaleic anhydride. Water was removed by evaporation until the residue hadan acid number of 35. About 70 parts of the cooled polyester reactionproduct was mixed with 30 parts of styrene.

Fifty parts of the linear copolymer were blended with 50 parts of thelinear polyester resin. The resulting blend was spread into a filmhaving a thickness of 3 mils, and the film was bombarded with a standardelectron accelerator with a radiation of 20 megarads in seconds. Thesurface of the film obtained was tack-free and mar-resistant.

EXAMPLE 2 To a 5 liter reaction vessel equipped with a thermometer, gasinlet valve, inlet funnels, electrical heating coils, mechanicalagitator and a reflux condenser, there was introduced 170 grams oftetrahydrofuran. Thereafter, the temperature of the tetrahydrofuran wasraised to 140F., and there was added under a blanket of nitrogen amixture of 260 grams styrene, 80 grams of methacrylonitrile, and 9 gramsof benzoyl peroxide. Simultaneously through a separate funnel, 100 gramsof styrene isocyanate dispersed in an additional 170 grams oftetrahydrofuran were introduced into the reactor. All reactants wereslowly added to the reaction vessel over a 4-hour period. The reactorcontents were continuously agitated and nitrogen gas was continuouslysparged through the reactor during the addition. The contents of thereaction vessel which comprised a reaction mixture of the componentsabove described was held at 140F. for an additional 6 hours after all ofthe components had been added to the reaction vessel. During thisperiod, there was formed a linear, saturated ester-free polymer backbonecontaining a plurality of isocyanate groups pendant from the backbone.

The reactor was then cooled and there was added 690 grams of styrenecontaining 0.6 gram of quinone, the latter serving as an inhibitor. Thetetrahydrofuran was removed from the bulk of the liquid phase of thereaction mixture by stripping in vacuo at a temperature of 125F. Thetemperature of the reaction mixture was then raised to 130F., and therewas added, while nitrogen was continuously sparged through the reactorand the reaction mixture was continuously agitated, 40 grams of allylalcohol. The addition was carried out over a 4-hour period after whichthere was formed a linear polymer consisting of an unsaturatedester-free backbone having pendant therefrom through urethane linkage aplurality of ethylenically unsaturated groups which were allyl alcoholresidues. The linear polymer was dispersed in styrene. The polymer hadan average molecular weight of approximately 30,000, as determined bygel phase chromatographic techniques.

A polyester resin was prepared by reacting equi-molar amounts ofethylene glycol and maleic anhydride with water removal until theresidue had an acid number of 35. About 70 parts of the resultingcondensation resin product was dissolved in 30 parts of styrene. Seventyparts of this resin were blended with 30 parts of the copolymerdispersion described in the first two paragraphs of this example, and afilm of the resulting product cured as described in Example 1. Thesurface of the cured film was tack-free.

When styrene solutions of the polyester resins described in Examples 1and 2 were cast into films without prior substitution by blending of thecopolymers described in these Examples and cured with the same radiationmeans and dose, the cure of the film surface was inhibited as evidencedby a tacky adhesive surface.

EXAMPLE 3 v To a one gallon pressure autoclave equipped with athermometer, a gas inlet valve, heating and cooling coils, mechanicalagitator, and inlet funnels for introducing inert gas and reactants,there is added 1,000 grams of xylene. Into a separate container, thereis mixed under a blanket of nitrogen, 800 grams of styrene, 150 grams ofmethacrylonitrile, and 10 grams of benzoyl peroxide. Fifty grams ofmethyl vinyl ether were charged to a nitrogen pressure bomb. The mixtureand the methyl vinyl ether were charged into the autoclavesimultaneously through separate funnels while the contents werecontinuously agitated and the temperature maintained at 280F. and at apressure of l50 lbs. psig. Prior to and during the addition. of thereactants to the autoclave, a blanket of gaseous nitrogen is maintainedand the contents are maintained under continuous agitation for 16 hoursafter which time substantially all of the styrene, methacrylonitrile,and methyl vinyl ether have polymerized. The contents of the reactionvessel then consist of a dispersion of approximately 1,000 grams of alinear polymer having a saturated ester-free backbone and which containsmethoxy (e.g., methyl ether groups) pendant from an external to thepolymer backbone. When a portion of the sample is withdrawn and theaverage molecular weight determined by gel phase chromatographictechniques, the polymer has an average molecular weight of about 50,000.The temperature of the contents of the autoclave is decreased to 180F.The pressure is psig., and thereafter, 99.7 grams of hydroxyethylacrylate containing 0.015 weight percent of hydroquinone and 10 grams ofsulfuric acid are simultaneously added over a period of 30 minutes whileagitation and heating are continued. Heating and agitation are continuedfor an additional hour until the hydroxy ethyl acrylate has undergonetransetherification with the pendant methoxy groups to form a polymerhaving a plurality of pendant ethyl acrylate groups which containethylenic unsaturation.

During the transetherification reaction, the methoxy moiety reacts withthe hydroxy] groups of the hydroxyethyl acrylate to form methanol. Atthe conclusion of the reaction, the methanol is removed by heating themixture in vacuo and 500 grams of the xylene are also stripped bydistillation in vacuo and 1,073 grams of styrene containing 0.015 weightpercent of hydroquinone are added to the polymer dispersion. Theremaining xylene is then stripped to provide a liquid polymercomposition containing 50 percent solids in which the solids consistessentially of a saturated polymer backbone having a plurality ofpendant ethylenically unsaturated groups which are etherified hydroxyethyl acrylate residues and are attached through ether linkage to thebackbone. The linear polymer is dispersed in styrene.

Fifty parts of the linear copolymer were blended with 50 parts of thelinear polyester resin. The resulting blend was spread into a filmhaving a thickness of 3 mils, and the film was bombarded with a standardelectron accelerator with a radiation of 20 megarads in 5 seconds. Thesurface of the film obtained was tack-free and mar-resistant.

EXAMPLE 4 To a 5 liter reaction vessel equipped with a thermometer, agas inlet valve, heating and cooling coils, mechanical agitator, refluxcondenser, and inlet funnels for introducing inert gas and reactants,there is added 100 grams of tetrahydrofuran. In a separate container,there is mixed 800 grams of styrene, l00 grams of acrylonitrile, 100grams of methallyl amine, and 10 grams of lauroyl peroxide. This mixtureis charged into the reactor over a period of 4 hours under continuousagitation and nitrogen sparge while the contents of the reactor aremaintained at F. Thereafter, the contents of the reaction vessel areheld at this temperature under continuous agitation and nitrogen spargefor an additional 12 hours until the polymerization reaction iscompleted. A portion of the sample is withdrawn and the averagemolecular weight, determined by gel phase chromatographic techniques, isfound to be 45,000. The polymer is a linear saturated ester-freeterpolymer having amine groups pendant from the linear backbonedispersed in tetrahydrofuran.

The temperature of the contents of the reaction vessel is decreased to78F. and thereafter, while nitrogen sparge and agitation are continued,398 grams of glycidyl methacrylate containing 0.015 weight percenthydroquinone are added over a period of about 60 minutes while thecontents of the reaction vessel are maintained at the last-mentionedtemperature, and continuous agitation and nitrogen sparge aremaintained. The resulting product is a linear polymer consisting of asaturated ester-free backbone having pendant therefrom through aminelinkage a plurality of ethylenically unsaturated groups comprisingglycidyl methacrylate residues.

One-half of the tetrahydrofuran is removed from the polymer by strippingin vacuo and thereafter, 1,398 grams of styrene containing 0.015 weightpercent hydroquinone are added to the polymer. The remainingtetrahydrofuran is removed by repeating the stripping operation. 7

The resultant product is a thennosettable liquid consisting of adispersion of a linear polymer which is unsaturated by virtue of aplurality of ethylenically unsaturated groups pendant from the backboneand a copolymerizable vinyl monomer (e.g., styrene).

A polyester resin was prepared by reacting equi-molar amounts ofethylene glycol and maleic anhydride with water removal until theresidue had an acid number of 35. About 70 parts of the resultingcondensation resin product was dissolved in 30 parts of styrene. Seventyparts of this resin were blended with 30 parts of the resin dispersiondescribed in the first four paragraphs of this example, and a film ofthe resulting product cured as described in Example 1. The cured filmobtained was tack-free and mar-resistant.

EXAMPLE To the reaction vessel described in Example 4, there is added1,000 grams of toluene. In a separate container, there is mixed under ablanket of nitrogen, 800 grams of styrene, 100 grams ofmethacrylonitrile, 100 grams of acrylamide, and grams of benzoylperoxide. This mixture is charged into the reactor over a period of 4hours under continuous agitation and nitrogen sparge while the contentsof the reactor are maintained at 240F. The temperature, agitation, andnitrogen sparge are maintained in the reactor for an additional 12 hoursuntil polymerization is completed. Thereafter, a portion of the sampleis withdrawn and the average molecular weight, determined by gel phasechromatography, is found to be approximately 45,000. The polymerobtained is a substantially linear saturated ester-free terpolymerhaving pendant amide groups external to the backbone. The temperature ofthe contents of the reaction vessel is then decreased to 230F. and whilenitrogen sparge and agitation are continued, 98 grams of crotonaldehydeand 1 gram of sulfuric acid catalyst are added to the reaction mixtureover a 30-minute period.

The reactor is held under these conditions for an additional 2 hoursuntil the crotonaldehyde has reacted with the dispersion to form apolymer having crotonaldehyde residues, thereby providing ethylenicunsaturation. I

Five hundred grams of toluene are stripped in vacuo from the polymerdispersion and 1,098 grams of styrene containing 0.015 weight percenthydroquinone are added to the polymer dispersion. The remainder of thetoluene is then removed by stripping to provide a liquid polymercomposition containing 50 percent solids consisting essentially of alinear saturated ester-free polymer backbone having a plurality ofethylenically unsaturated groups comprising residues of crotonaldehyde,which are pendant from the backbone through amide linkage and which aredispersed in the styrene.

Fifty parts of the linear copolymer were blended with 50 parts of thelinear polyester resin dispersion described in Example I. The resultingblend was spread into a film having a thickness of 3 mils, and the filmwas bombarded with a standard electron accelerator with a radiation ofmegarads in 5 seconds. The surface of the cured film obtained wastack-free and mar-resistant.

EXAMPLE 6 4 To a reaction vessel, there was added 400 grams of ethyleneglycol monoethyl ether.

To a separate container, there was mixed 220 grams of styrene, 60 gramsof acrylonitrile, 120 grams of dihydroxypropyl maleate and 4 grams ofbenzoyl peroxide. This mixture was charged into the reactor over aperiod of 2 hours under continuous agitation while the contents of thereactor were maintained at 185F. The contents of the reaction vesselwere held under the nitrogen sparge, continuously agitated, andmaintained at 185F. for 10 hours until polymerization had beencompleted. A portion of the sample was withdrawn and the averagemolecular weight, determined by gel phase chromatography, was found tobe 85,000. The thermoplastic polymer was a linear saturated ester-freeterpolymer having pendant hydroxyl groups.

The temperature of the contents of the reaction vessel was increased to225F. and thereafter while the nitrogen sparged and agitation wascontinued, 518.4 grams of maleic anhydride and a small amount of lithiumcarbonate were added over a period of about 60 seconds, then 308.4 gramsof propylene oxide were added while the contents of the reaction vesselwere maintained at a reflux temperature of 250F. using adequate coolingmeans to prevent oxide loss. The resulting product was a linear polymerconsisting of a saturated esterfree backbone having pendant therefromthrough ester linkage with the hydroxyl groups, a plurality ofhydroxypropyl maleate groups dispersed in ethylene glycol monoethylether hydroxypropyl maleate.

The contents of the reaction vessel were increased to 280F. and 16.3grams of piperidene, an isomerization catalyst, were added. The contentswere agitated and held for 4 hours at this temperature after which thecontents of the reaction vessel were cooled to 240F. and consistedessentially of the linear polymeric backbone on which pendant maleicacid groups at-' tached through ester linkages had been converted tofumarate groups. The reaction mixture was then cooled to 240F. and 0.34grams of hydroquinone were dispersed over a 5-minute period withagitation. The resulting polymer solution was then reduced in 696 gramsof styrene. The resulting product consisted of a linear thermoplasticpolymer having engrafted thereon through ester linkage a plurality ofhydroxypropyl fumarate groups. The average molecular weight of thepolymer, determined by gel phase chromatography, was found to be100,000.

Fifty parts of the linear copolymer were blended with 50 parts of thelinear polyester resin dispersion described in Example l. The resultingblend was spread into a film having a thickness of 3 mils, and the filmwas bombarded with a standard electron accelerator with a radiation of20 megarads in 5 seconds. The surface of the cured film obtained wastack-free and mar-resistant.

EXAMPLE 7 Four hundred fifty grams of 2-ethoxy ethanol were added to thereaction vessel described in Example 1.

The following ingredients in the amounts listed below were added andmixed under a blanket of nitrogen in a separate container.

Ingredients Grams Hydroxypropyl methacrylate Ethyl acrylate 400 Styrene500 Benzoyl peroxide l5 Tertiary butyl perbenzoate 15 The 2-ethoxyethanol in the reactor was heated to reflux and the above mixture wascharged to the reactor over a 3- hour period while the contents weremaintained under continuous agitation and at a temperature of i 3C.Prior to and during the addition of the mixture gaseous nitrogen wascontinuously sparged through the reactor and its contents. After theaddition of the mixture was completed, the reactor contents weremaintained under conditions of reflux, continuous agitation and nitrogensparge for an additional hour, after which, while heating and agitationwere continued. Then one gram of additional tertiary butyl peroxide wascharged to the reactor and contents were maintained under the sameconditions for an additional 4-hour period until all of thehydroxypropyl methacrylate, ethyl acrylate and styrene had polymerizedto form a linear ester-free backbone containing a plurality of pendanthydroxyl groups. The polymer has an average molecular weight of about20,000.

Thereafter while agitation and nitrogen sparge were continued, thetemperature of the reactor contents was heated about to 100C. and 558grams of maleic anhydride were added over a 30-minute period. During theaddition, the temperature of the contents of the reactor contentsincreased to 130 3C. and heating and agitation were continued for anadditional 30 minutes after completion of the addition of the maleicanhydride. There was then added 2.4 grams of lithium carbonate and 364grams of propylene oxide,the latter being added over a l-hour period. I

The contents of the reactor were maintained for an additional hour underthe same temperature, agitation and nitrogen sparge conditions and anadditional 558 grams of maleic anhydride were added overa 60-minuteperiod, then 364 grams of additional propylene oxide were added, the contents of the reactorbeing held for an additional 60 minutes after theaddition of the propylene oxide. Thereafter another additional 5 58grams of maleic anhydride were charged to the reactor over a 30-minuteperiod and the contents in the-reactor were held under theabove-described reaction conditions for an additional 30 minutes afterwhich another additional 364 grams of propylene oxide were added over al-hour period and the contents of the reactor were maintained under thesame reaction conditions for an additional 60 minutes.

The resultant reaction mixture consisted essentially of a polymercomprising a linear saturated ester-free backbone having pendanttherefrom through ester linkage a linear residue consisting of threesuccessive hydroxypropyl maleate esters. In other words, the pluralityof pendant unsaturated groups had polyunsaturation by virtue of thesuccessive addition of three mols of maleic unsaturation throughesterification effected by propylene oxide addition. The polymer wasdispersed in the cellusolve tri-ester, the ester also containingpolyunsaturation by virtue of the successive formation of three mols ofhydroxypropyl maleate. The resultant product was converted from maleateunsaturation to fumarate unsaturation by the addition of 42 grams ofpiperidene and 0.086 grams of hydroquinone and heating the mixture to1351- 3C. for 4 hours to isomerize the maleate moieties to fumarate.

A film of the resultant polymer composition was applied to a metal plateat a thickness of 0.5 mils and subjected to 2 megarads of 500 kiloelectron volt radiation in an atmosphere of nitrogen. The resultingcured film was a tack-free and marresistant coating.

This application contains subject matter related to that contained infive copending patent applications Ser. No.s 798,439, 798,458, 798,461,798,470, and 798,769, filed simultaneously with the instant applicationand assigned to the same assignee.

What is claimed is:

l. in a process for crosslinking an unsaturated air-inhibited resin,wherein said unsaturated air inhibited resin is the reaction product ofa polycarboxylic acid and a polyol having an average molecular weightbelow about 6,000 with a vinyl compound copolymerizable therewith bymeans of radiation selected from the group consisting of a beam fromelectronemitting means and micro-wave energy with a beam fromelectron-emitting means wherein curing occurs by the addition ofunsaturated molecules one to another, the improvement for reducing airinhibition which comprises:

substituting for at least about 5 weight percent of said unsaturatedair-inhibited resin a linear copolymer having an average molecularweight greater than the average .molecular weight of said unsaturatedresin wherein the backbone is the addition polymer of A. from about 40to about weight percent of at least one monomer selected from the groupconsisting of: l. mono ethylenically unsaturated substituted andunsubstituted hydrocarbons, 2. mono ethylenicallyunsaturated esters oforganic and inorganic acids, 3. halides of mono ethylenicallyunsaturated organic alcohols, and I 4. mono ethylenicallybunsaturatednitriles, and B. from about 10 to a out 20 weight percent of an a, )9-

mono ethylenically unsaturated mono functional monomer selected from theclass consisting of oxiranes, ethers, hydroxyl compounds, isocyanates,amides, and

primary and secondary amines and where said ethylenically unsaturatedmonomers are pendant from said backbone by, virtue of the reaction of asubstantially stoichiometric amount of said a, B-mono ethylenicallyunsaturated mono functional monomer reactible with functional groupspendant from the backbone, said copolymer having an average molecularweight of from about 5,000 to about 225,000.

2. The process of claim 1 wherein said cross-linking is conducted in aninert atmosphere.

3. The process of claim 1 where, in said linear copolymer, the pluralityof ethylenically unsaturated groups are attached to the backbone throughester linkage.

4. The process of claim 1 where, in said linear copolymer, the pluralityof ethylenically unsaturated groups are attached to the backbone throughether linkage.

5. The process of claim 1 where, in said linear copolymer, thepluralityof ethylenically unsaturated groups are attached to thebackbone through urethane linkage.

6. The process of claim 1 where, in said linear copolymer, the pluralityof ethylenically unsaturated groups are attached to the backbone throughamine linkage.

7. The process of claim 1 where, in said linear copolymer, the pluralityof ethylenically unsaturated groups are attached to the backbone throughamide linkage.

2. The process of claim 1 wherein said cross-linking is conducted in aninert atmosphere.
 2. mono ethylenically unsaturated esters of organicand inorganic acids,
 3. halides of mono ethylenically unsaturatedorganic alcohols, and
 3. The process of claim 1 where, in said linearcopolymer, the plurality of ethylenically unsaturated groups areattached to the backbone through ester linkage.
 4. The process of claim1 where, in said linear copolymer, the plurality of ethylenicallyunsaturated groups are attached to the backbone through ether linkage.4. mono ethylenically unsaturated nitriles, and B. from about 10 toabout 20 weight percent of aN Alpha , Beta -mono ethylenicallyunsaturated mono functional monomer selected from the class consistingof oxiranes, ethers, hydroxyl compounds, isocyanates, amides, andprimary and secondary amines and where said ethylenically unsaturatedmonomers are pendant from said backbone by virtue of the reaction of asubstantially stoichiometric amount of said Alpha , Beta -monoethylenically unsaturated mono functional monomer reactible withfunctional groups pendant from the backbone, said copolymer having anaverage molecular weight of from about 5,000 to about 225,000.
 5. Theprocess of claim 1 where, in said linear copolymer, the plurality ofethylenically unsaturated groups are attached to the backbone throughurethane linkage.
 6. The process of claim 1 where, in said linearcopolymer, the plurality of ethylenically unsaturated groups areattached to the backbone through amine linkage.
 7. The process of claim1 where, in said linear copolymer, the plurality of ethylenicallyunsaturated groups are attached to the backbone through amide linkage.